Gas quality, quantity, and energy measurement in the context of fuels, particularly in custody transfer from a pipeline or source, requires sample takeoff and conditioning. It is known that variations in sample measurements may be caused, for example, by fluid flow irregularities, component partitioning, and/or phase separation either before or during the sample extraction process. The presence of flow pulsations, non-laminar flow, and extracted sample lag time are some of the recognized problems that undermine sufficient sample flow uniformity to prevent accurate analysis.
Standard sampling practices in the LNG industry, particularly in the context of custody transfer operation, typically are made when the LNG is at specified levels in a static storage container or based on observations of the physical flow state in a pipeline when a stable flow rate is believed to have been achieved. During periods of instability or erratic flow, sample extraction and analysis is typically suspended until acceptable conditions resume. Governing standards for the sampling of liquefied natural gas, such as ISO 8943:2007, Chapter 7.1 states that sampling should only occur during “ . . . that period of time during which the flow rate is sufficiently stable . . . ” The standard does not define any particular method to quantify the stated “stable” condition. However, in the absence of a readily apparent problem, the steady state flow determination conventionally is made only after the fact. That is, only after passing through the analyzer and detecting variations in obtained analytical results beyond a permissible threshold does the stability of the sample flow become suspect. Consequently, the validity of the obtained results is problematic and the accuracy of the results for context energy audits in custody transfer or the like often becomes unreliable. Existing systems and apparatus for flow analysis of fluids in pipelines do not address the problem associated with sample takeoff during unstable flow conditions and therefore overlook the resulting problems with measurement/analytical accuracy.
What is needed is a system integrated or associated with sample takeoff equipment for substantially coincidental verification of a steady flow state of the sampled fluid.